[Feature request] Support self-hosted registry out of the box.

[m3thom]

To utilize all kamal features (e.g., zero downtime, rollback, etc.), I need a registry.

In my case, I have only one server right now and I don't want to use any external registry provider. So, I want to host both my application and my registry on the same server.

From my understanding, it's fairly easy to host a private registry Docker Distribution. As of now, I believe the Kamal ecosystem could support this.

We could categorize this under the kamal accessories section since we don't need to build the registry. We could use kamal-proxy to manage the network and TLS.

For the authentication setup, there might be some manual steps involved, but it's quite straightforward.

$ mkdir auth
$ docker run \
  --entrypoint htpasswd \
  httpd:2 -Bbn testuser testpassword > auth/htpasswd

While these steps need to be done manually, is it possible to support this self-hosted registry feature out of the box?

Thank you for this amazing library! I really want to use it for my application!